The invention relates to a method for manufacturing highly heat-resistant dielectrics on the basis of organic polymers on a substrate.
Organic dielectrics are non-conducting substances used primarily in microelectronics as planarizing insulating layers and as passivating layers in the manufacture of components, for instance, in the multilayer wiring of integrated circuits (ICs). The planarizing properties are required in order to abate the unevenness of the surface of the substrate which results from successive process steps, thereby making possible a secure multilayer construction.
Dielectrics of the above mentioned type which serve as passivating insulating layers between conducting and/or semiconducting materials, remain in the components and must therefore meet a number of requirements. First, these insulating layers must exhibit high-temperature resistance so that they can be used in modern methods such as sputtering, dry etching, plasma etching and reactive ion etching which, in part, require high temperatures. They should also exhibit good electrical properties such as a low dielectric constant and a small loss angle. In addition, these insulating layers should exhibit low moisture absorption, be resistant against alkaline developers and have the capability to be produced with high purity so that they contain ionic impurities only in the ppm or sub-ppm range. These properties are required since high moisture absorption has a negative influence on the electrical characteristics of the insulating layers and ionic impurities have an adverse influence upon the electrical characteristics, the reliability in the components, and the moisture behavior of the layers.
Conventional temperature-resistant organic insulating layers (i.e., dielectrics typically consist of polymers on the basis of polyimides (see, for instance: "35th Electronic Components Conference", Washington, U.S.A., May 20 to 22 (1985)-Conference Support 1985, pages 192 to 198). For manufacturing high-temperature resistant layers one generally starts out with polymer precursor stages in the form of soluble polyamidocarboxylic acids which are applied to the substrate and are subsequently converted into polyimides by an annealing process (see in this connection: DE-OS 28 48 034).
However, polyimides have only little resistance against alkaline developers. They are actually decomposed by alkali. In addition, they exhibit a relatively high moisture absorption (3.8% for a relative moisture of 0% to 100%, at 25.degree. C.), mainly due to their polar carbonyl groups. The electrical characteristics of polyimides are also not satisfactory: dielectric constant .epsilon. (at 25.degree. C., 0% relative humidity)=3.35; loss angle tan .delta. (at 25.degree. C., 0% relative humidity)=4.1.times.10.sup.-3, tan .delta. (at 25.degree. C., 100% relative humidity)=15.times.10.sup.-3.
It is an object of the invention to develop a method for manufacturing organic dielectrics on a substrate in which the dielectrics exhibit a high temperature resistance, good electrical properties, resistance to alkali, low moisture absorption and high purity.